1. Technical Field
The present invention relates in general to hard disk drives and, in particular, to an improved system, method and apparatus for determining the track pitch in a hard disk drive to satisfy the requirements of both off-track capacity and adjacent track erasure.
2. Description of the Related Art
Hard disk drives provide data storage for data processing systems in computers and servers. Disk drives are also becoming increasingly pervasive in media players, digital recorders, and other personal devices. Advances in disk drive technology have made it possible for a user to store an immense amount of digital information on increasingly smaller areas, and to selectively retrieve and alter portions of such information almost instantaneously. Particularly, recent developments have simplified disk drive manufacturing while yielding increased track densities, thus promoting increased data storage capabilities at reduced costs.
Hard disk drives rotate high precision media, such as an aluminum or glass disk coated on both sides with thin films, to store information in the form of magnetic patterns. Electromagnetic read/write heads suspended or floating only fractions of micro inches above the disk are used to either record information onto the thin film media, or read information from it.
A read/write head may write information to the disk by creating an electromagnetic field to orient a cluster of magnetic grains, known as a bit, in one direction or the other. In longitudinal magnetic recording media applications, a magnetic recording layer has a magnetic c-axis or easy axis parallel to the disk plane. As the disk drive industry is transitioning to perpendicular recording technology, adjustments are being made to adapt the disk media so that the magnetic easy axis of the cobalt alloy recording layers grow perpendicular to the disk plane. Hexagonal close packed cobalt alloys are typically used as a magnetic recording layer for perpendicular recording.
To read information, magnetic patterns detected by the read/write head are converted into a series of pulses that are sent to the logic circuits to be converted to binary data and processed by the rest of the system. To write information, a write element located on the read/write head generates a magnetic write field that travels vertically through the magnetic recording layer and returns to the write element through a soft underlayer.
Hard disk drive designs require adequate off-track capability (OTC) and sufficiently small adjacent track interference or erasure (ATI). Both OTC and ATI are sensitive to the track pitch on the magnetic media disk: each gets worse as the track pitch decreases. Despite those relationships, further reductions in track pitch are required for future generations of disk drives in order to increase the overall performance of drives. Unfortunately, OTC and ATI are affected by the track pitch in very different ways.
In current disk drive design, only OTC is taken into consideration when track pitch is determined for a disk drive. This can lead to high ATI failure rates. Conventional solutions to this ATI issue use encroachment tests only after the track pitch is set for the disk drive. See, e.g., U.S. Pat. No. 7,227,708, and US Pat. App. Pub. 2008/0062550. For example, a victim track may first be written and an aggressor track is subsequently written multiple times. The ATI is then obtained from the signal or error rate loss in the victim track. When failure occurs during such ATI tests, the track pitch is adjusted on a trial and error basis. This process is repeated until an acceptable overall performance for the drive is attained. Although these solutions are workable, an improved solution for determining the track pitch in hard disk drives would be desirable.